Optical internal quality analyzer

ABSTRACT

A system for measuring the optical density of an object in which the object is illuminated with light of different wavelengths in a continuous sequence. The level of light transmitted through or, alternatively, reflected by the object during each illumination is measured by means of a photodetector. The photodetector output for each wavelength is converted in an analyzer unit to a measurement of transmissive or reflective optical density. The analyzer unit is controlled by selected synchronization signals which are generated during illumination and correspond to the illumination sequence. The analyzer unit samples and stores values of optical density at a pair of wavelengths corresponding to the synchronization signals and produces a digital output representing either absolute optical density at one of the wavelengths or the difference between the optical densities at the pair of wavelengths.

United States Patent [191 Ganssle et a1.

[ OPTICAL INTERNAL QUALITY ANALYZER [75] Inventors: Eugene R. Ganssle,Silver Spring; Donald R. Webster, Laurel, both of Md.

[73] Assignee: Neotec Corporation, Rockville,

[22] Filed: Mar. 15, 1972 [21] Appl. No.: 234,843

[52] US. Cl. 356/188, 356/189, 356/195, 356/205, 356/212, 356/244 [51]Int. C1.G01j3/48, GOln 21/22, GOlj 21/48 [58] Field of Search 356/173,188, 189, 356/195, 204, 205, 209, 210, 211, 212, 244

Lord 356/205 Biesele, Jr 356/212 ANALYZER UNIT [ Oct. 16, 1973 PrimaryExaminerDavid Schonberg Assistant Examiner-V. P. McGraw Attorney-JosephM. Lane et a1.

[5 7] ABSTRACT A system for measuring the optical density of an objectin which the object is illuminated with light of different wavelengthsin a continuous sequence. The level of light transmitted through or,alternatively, reflected by the object during each illumination ismeasured by means of a photodetector. The photodetector output for eachwavelength is converted in an analyzer unit to a measurement oftransmissive or reflective optical density. The analyzer unit iscontrolled by selected synchronization signals which are generatedduring illumination and correspond to the illumination sequence. Theanalyzer unit samples and stores values of optical density at a pair ofwavelengths corresponding to the synchronization signals and produces adigital output representing either absolute optical density at one ofthe wavelengths or the difference between the optical densities at thepair of wavelengths.

13 Claims, 3 Drawing Figures PATENTEDUCT 16 I975 SHEET 1 BF 2 F/G.l.

FIG. 3.

ANALYZER UNIT 1 OPTICAL INTERNAL QUALITY ANALYZER BACKGROUND OF THEINVENTION The invention relates generally to the field of instru mentsfor measuring light transmittance of reflectance, and more particularlyto improve apparatus for measuring and comparing optical densities oforganic materials at various wavelengths.

Prior researchers have confirmed that nondestructive light transmittancetests on various agricultural products can be indicative of theirinternal quality. Predictable transmittance characteristics have nowbeen attributed to variousstructural properties including specifichorticultural defects such as water core in apples and hollow hearts inpotatoes. Prior art devices for producing such measurements lackedversatility and depended to a high degree on manual operation andadjustment to obtain readings for different size objects at severaldifferent wavelengths.

SUMMARY OF THE INVENTION Accordingly, the general purpose of theinvention is to measure and display automatically transmittance orreflectance levels at several different wavelengths of light. Anotherobject of the invention is to measure and display differences in opticaldensity for several pairs of wavelengths. A further object of theinvention is to simplify the positioning of objects for uniformmeasurements of optical density. Still another object of the inventionis to enable instantaneous switching among measurements of absoluteoptical density at different wavelengths and differences in opticaldensity for several pairs of wavelengths.

These and other objects of the invention are achieved by providing aself positioning carriage having a cushioned platform on which testobjects such as whole apples can be placed. The platform contains acentrally located photodiode detector. The test object is illuminated bylight from a high intensity source sequentially filtered by acontinuously rotating disc having a plurality of optical filters.Synchronizing means are located on the disc to indicate, by means of adetection system, which one of the filters is in operating position,i.e., in the optical path, at any given time. In one embodimentapertures are spaced about the disc and the detection system includeslight sources and photodetectors aligned on opposite sides of the wheelto provide synchronization (sync) signals.

The output of the photodiode detector on the test platform representsthe intensity of transmitted light, but the ease of transmitting lightthrough the object is read in terms of transmissive optical density(OD), related to intensity by the formula D log (Ii/It, where I, is theintensity of incident light or the measured light intensity with nospecimen, and I, is the intensity of transmitted light or the measuredlight intensity through the specimen. Differences between OD readingsfor a particular pair of wavelengths are the most meaningful andcharacteristic measurement for certain types of internal qualityevaluation, such as the maturity of apples. To produce a directtransmissive optical density difference (AOD) reading, an analyzer unitprovides a logarithmic amplifier which receives the photodiode detectoroutput. The output of the logarithmic amplifier is linearly related toOD. A pair of sample and hold circuits receives the output of thelogarithmic amplifier. A digital counter operated by the sync signalsprovides parallel outputs, each marking the time when a correspondingfilter passes through the optical path. One counter output is chosen togate each sample and hold circuit. The continuously updated outputs ofthe hold circuits are fed to opposite inputs of a differential amplifierwhose analog outputs is linearly related to AOD. The differentialamplifier output is converted to digital form for driving a digitaldisplay of AOD for the selected pair of wavelengths. To read absolute ODfor a single filter, the output of one of the sample and hold circuit isinhibited, for example, by grounding the circuit.

Useful measurements may also be obtained by locating photodiodes toreceive light reflected from the specimen during the illuminationsequence. The photodiode output is fed to the analyzer unit whichoperates in the same manner as for the transmittance measurement AOD.However, in this case the reading is based on reflectivity of thespecimen. The case of reflecting light from the specimen is measured interms of reflective optical density (RD),'which is defined herein by theformula RD log (I /I where I, represents the intensity of incident lightand I, represents the intensity of reflected light. By sampling theintensity of reflected light at different wavelengths, the analyzer unitreads out either absolute RD, based on the logarithm of reflectiveintensity for one wavelength, or the difference between reflectiveoptical densities (ARD) for a pair of wavelengths.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block and schematicdiagram illustrating one embodiment of the invention.

FIG. 2 is a block and schematic diagram illustrating the electronicanalyzer unit of FIG. 1 in more detail.

FIG. 3 is a partial schematic diagram illustrating another embodiment ofthe invention in which the device of FIG. 1 is adapted to measurereflectance.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 of thedrawings, a carriage assembly 10 comprises a pair of guide rails 11 and12 with a carriage l4 slidably mounted on guide rail 11. A specimenplatform 16 is secured at one end to the top of carriage l4 and isnotched at the other end to slidably engagerail 12 preventing lateraldisplacement. A lower cushion 17, located on top of platform 16,provides a mount for the specimen to be tested. Cushion 17 has a centralaperture over which an object such as an apple is placed. Aphotosensitive element 19 is positioned in the aperture for sensinglight transmission through the specimen, For raising and loweringplatform 16, an upper arm 20 is pivotally connected at one end to guiderail 11 above carriage 14, or to any other non-moving part of thesystem. The other end of upper arm 20 is pivotally connected by a pin 21to one of each of a pair of parallel lower arms 22. A spring 23 urgesarm 20 towards arms 22 about pin 21. The other ends of lower arms 22 arepivotally connected to opposite sides of sliding carriage 14. A handle24 is rigidly connected at one end to upper arm 20. When the free end ofhandle 24 is moved, upper arm 20 is caused to pivot about its fixedpoint of connection. At the same time, carriage 14 slides along guiderail 11 because of itspivotal connection to the other end of upper arm20 by means of lower arms 22. Thus, movement of handle 24 alters thelevel of platform 16 which is secured to carriage 14 with the platformbeing movable between a fixed lower position, in which the specimen isloaded onto cushion 17, and an upper position defined by the location ofan annular fixed cushion 26, in which the specimen is analyzed in amanner to be explained in detail later.

In order to move platform 16 to the above-mentioned fixed lowerposition, handle 24 is rotated clockwise, as viewed in FIG. 1, past thepoint where upper arm 20 is aligned with lower arms 22, until theinterconnected ends of arm 20 and arms 22 rest against rail 11. In thisposition, spring 23 would be located slightly to the right of pin 21,causing arm 20 and arm 22 to be maintained in a locked, over-centerrelationship despite release of the handle 24. After a specimen ismounted on lower cushion 17, handle 24 is rotated counterclockwise, backtowards it original position raising platform 16 to a level at which themounted specimen is forced against upper cushion 26 which serves as astop. The platform is retained in the upper position, by spring 23,after release of handle 24.

An illuminating system, shown in general by the reference numeral 27 inFIG. 1, is provided in a spaced relation to carriage assembly 10, andcomprises a filter wheel 28, in the form of an apertured disc in whichfour different optical filters 29, 30, 31 and 32 are located equallyspaced about a central axle 33. Filter wheel 28 is belt driven at acontinuous speed by a motor 36. A fixed high intensity lamp 37 is spacedappropriately from axle 33 and is arranged to shine light throughfilters 29-32 as they pass in sequence beneath lamp 37. A fixed,converging lens system 38 is located in the optical path between lamp 37and the upper cushion 26 and is adapted to focus the light from lamp 37onto the specimen.

Filter wheel 28 has a aperture 41 provided therethrough and located at afirst radial distance angularly between two adjacent filters. A lightsource 42 is provided above filter wheel 28 and is spaced from axle 33by the first radial distance. When aperture 41 is in mg istrationdirectly below light source 42, light is passed to a photosensitiveelement 43 rigidly aligned with light source 42 below filter wheel 28.As the wheel spins, one output pulse from element 43 marks everycomplete revolution. I

Four other apertures 44 are located respectively beside filters 29-32 ata second radial distance from axle 33 with this second radial distancebeing greater than the first radial distance. Another light source 46and photosensitive element 47 are aligned on opposite sides of filterwheel 28 at the second radial distance from axle 33. As a result, eachtime one of filters 29-32 registers with lamp 37, a corresponding one ofapertures 44 registers with light source 46 permitting light to pass toelement 47 and an output pulse to be generated. Thus, element 47produces four output pulses per revolution of wheel 28.

The outputs from the photosensitive elements 43 and 47 and from thephotodetector 19 are connected to an analyzer unit 50 which is shown indetail in FIG. 2. In particular, the unit 50 includes a longarithmicamplifier 52 which receives the output from the photodetector 19 andproduces an output which is linearly related to absolute OD for thesequentially filtered light. A pair of sample and hold circuits 53 and55 are connected to receive the output of amplifier 52. In order tosample the sequential output of amplifier 52 at times corresponding tothe registration of a particular filter in the optical path a, circuitsS3 and 55 are controlled by a digital counter 57. Counter 57 receivesthe pulse outputs of photosensitive elements 43 and 47 as sync signals.The output of element 47 serves as a load input to counter 57 and theoutput of element 43 resets the counter to zero. Counter 57 has fourparallel outputs which are sequentially activated one at a time, andwhich correspond respectively to filters 29-32. The counter outputsprovide timing or gate pulses for sample and hold circuits 53 and 55.

Counter 57 is implemented so that only its first output is pulsed whenthe first output fromelement 47 is received. The second output ofcounter 57 is pulsed on receipt of the second pulse from element 47.After the third and fourth outputs of counter 57 have been individuallypulsed on the occurrence of the third and fourth outputs of element 47,element 43 produces one reset pulse, due to the completion of onerevolution of wheel 28. Accordingly, on the next output pulse fromdetector 47, the first counter output is again pulsed. The rest of thesequence is similarly repeated.

Switches 61, 62, 63 and 64 are located respectively in the counteroutput lines. A mode selector 71, which may be a manually operatedganged switch, can be activated to close either of two pairs of switches61 and 63, or 62 and 64. For example, if the latter pair of switches, 62and 64, are both closed as shown in FIG. 2, hold circuit 55 samples theoutput of the logarithmic amplifier at a time when the second filter,filter 29, for instance, is in the optical path and retains or storesthat value until, in the next cycle, the same filter is sampled again toupdate the output of hold circuit 55. Likewise, hold circuit 53 samplesthe amplifier output when the fourth filter is in position, forinstance, filter 31, and continues to update the value for the filtereach time it passes beneath lamp 37.

The output of hold circuit 53 is passed to one input of a differentialamplifier 81, while the output of hold circuit 55 is passed to thedifferential amplifiers opposite input. The output of amplifier 81 islinearly related to the algebraic difference, AOD, between the holdcircuit outputs at any given time. If the absolute OD for one particularfilter is desired, instead of AOD for two filters, the appropriate pairof switches for the counter outputs, including the one corresponding tothe desired filter, is activated, and the hold circuit which wouldreceive the data on the non-selected filter is grounded, or otherwiseinactivated, by means of switch 73 or 75. To provide an accuratelyreadable display, the analog output of differential amplfier 81 isconverted to digital form by converter 85 whose output drives a digitaldisplay 91 (FIG. 1) which typically comprises a three digit Nixie(trademark) tube display plus a sign.

The embodiment of FIG. 3 is adapted to measure reflectance instead oftransmittance and incorporates many of the components of the embodimentof FIG. 1, with the latter being given identical reference numerals. Inparticular, a specimen tray 100 containing nuts, for example, is placedon lower cushion 17. A housing or cylinder 102 with a diameter no largerthan that of lower and upper cushions 17 and 26 is mounted on top oflower cushion 17 co-axially with the optical axis a between lamp 37 andthe specimen. Four photodetectors 104 are mounted adjacent the upper endof cylinder 102, are spaced apart about the inner surface of cylinder102 and are inclined downwardly toward tray 100 to receive lightreflected from the specimen. In this manner, cylinder 102 serves as alight shield, a support for photodetectors 104, and a spacer betweencushions 17 and 26 for positioning platform 16 at a predetermined level.

The illuminating system 27 and its associated sync system, as well asanalyzer unit 50 and its components are used in an identical manner inthe embodiment of FIG. 3 as described in connection with the embodimentof FIG. 1. Also the electrical connections and operation of theembodiment of FIG. 3 will be identical to the arrangement of FIG. 2,with the exception that the outputs from the photodiode 104 are summedand connected to the logarithmic amplifier 51 of the analyzer unit 52 inplace of the output from the photodiode 19.

Therefore in the embodiment of FIG. 3 a pair of wavelengths (filters)are selected by mode selector 71, and analyzer unit 50 provides anoutput indicative of the difference between the logarithms of theintensity of reflected energy at two different wavelengths, termed thedifference in reflective optical density, ARD. As in the transmittancemeasurement of OD, switches 73 and 75 may be used to read out absoluteRD for one wavelength. Useful ARD measurements have been obtained usinginfrared wave-lengths to determine the moisture content of nuts.

It is understood that all of the components forming the instruments ofboth embodiments of the present invention will normally be mounted in acabinet or the like which is adapted to provide support for the fixedcomponents of the instrument and which accommodates the movablecomponents.

The operation of the instrument of the present invention will bedescribed in connection with the determination of the maturity of anapple using the transmittance measuring apparatus of the embodiment ofFIG. 1. The transmittance measurement by which ripe apples can best bedistinguished from immature apples is the value of AOD OD (at 690 nm) CD(at 740 nm) where nm represents nanometers of wavelength. Thisparticular AOD is dependent on chlorophyll content, which is indicativeof ripeness. For this measurement, two filters 29 and 31, for example,among the group of four filters 29-32 in wheel 28, must have peaktransmittances at 690 and 740 nm. The apple to be tested is placed onlower cushion 17 and raised to the upper position by handle 24. Lamp 37and sync light sources 42 and 46 are activated, and continuous rotationof wheel 28 is begun. The outputs of counter 57 (FIG. 2) whichcorrespond to the two selected filters 29 and 31 are passed respectivelyto control sample and hold circuits 53 and 55 by means of mode selector71. The AOD is read directly from display 91. AOD depends on therelative ease of transmitting these two wavelengths of light through theapple. Depending on the AOD reading, as compared to experimentalstandards derived from former experiments on the same type of apple, andtest apple is determined to be ripe or unripe.

Those skilled in the art will recognize that variations of each of theforegoing embodiments are permissible, without departing from the scopeof the present invention. For example, the filter wheel can be adaptedto circulate any required number of filters. The only difference in theelectronics would be that the number of selectable counter outputs wouldbe increased. A preamplifier may be necessary before logarithmicamplitier 52 to maintain a consistent scale for both transmissive andreflective readings. In addition, other sync signal systems arepossible, such as magnetic pick-ups or contact pick-offs. Light sources42 and 46 can be combined into one source, if desired. Alternatively,high intensity lamp 37 can be arranged to shine light through syncapertures 41 and 44 as well as filters 29-32.

The advantages of the invention are numerous. Optical densitymeasurement techniques are nondestructive. Thus, the same sample can bemeasured daily and its changes observed as a function of time. Thesimple operation permits the use of the device as either a researchinstrument or as a production tester. The multi-filter system allowstesting for two or more parameters simultaneously. The versatility ofthe measuring apparatus is greatly enhanced by the dual mode ofoperation, providing instantaneous switching from readouts of absoluteoptical density at each wavelength to optical density differences fortwo wavelengths. Moreover, the mechanical arrangement of the carriageassembly allows specimens of varying sizes to be readily accommodated ina convenient manner.

It will be understood that other changes in the details, materials,steps and arrangements of parts which have been herein described andillustrated in order to explain the nature of the invention, may be madeby those skilled in the art within the principle and scope of theinvention as expressed in the appended claims.

We claim:

1. Optical measuring apparatus, comprising a light source, a pluralityof optical filters, filter wheel means mounted for rotation between saidlight source and an object to be optically analyzed and carrying saidfilters for sequential registration thereof in the optical path betweensaid light source and said object, light sensitive means operativelypositioned to produce an output indicative of the light received fromsaid light source via said object, a logarithmic amplier operativelyreceiving the output of said light sensitive means, drive means forcausing regular rotation of said wheel means, first indexing meansformed on said filter wheel means for indicating each completerevolution of said wheel means, second indexing means formed on saidwheel means for indicating registration of each said filter in saidoptical path, means responsive to said first and second indexing meansfor providing corresponding first and second sinc signals, counter meansoperatively receiving said second sinc signal as a load input theretoand said first sinc signal as a reset input for producing paralleloutputs corresponding respectively to said filters, said counter meansproviding gate signals at each one of said parallel outputs when thecorresponding filter is in the optical path, a pair of sample and holdcircuit means each operatively receiving the output of said logarithmicamplifier and each controlled by a different one of said gate signals tosample the output of said logarithmic amplifier at times correspondingto the illumination of the object by light of one respective wavelength,and differential amplifier means operatively receiving the output ofeach of said circuit means for producing an output indicative of thedifference in optical density for the two respective wavelengths.

2. The apparatus of claim 1, wherein further including means forselectively inactivating one of said sample and hold circuit means sothat the output of said differential amplifier is indicative of opticaldensity for one of said filters.

3. The apparatus of claim 1, further comprising digital display means,and analog to digital converter means operatively receiving saiddifferential amplifier output for producing a digital output to saiddisplay means.

4. The apparatus of claim 1, further comprising support means foroperatively positioning said object be.- tween said illuminating meansand said light sensitive means so that said light sensitive meansproduces an output indicative of the level of light transmitted throughsaid object.

5. The apparatus of claim 4, further comprising linkage means for movingsaid support means to and from a predetermined position relative to saidilluminating means, and means cooperating with said linkage means formaintaining said position despite variations in the size of said object.

6. The apparatus of claim 5, wherein said maintaining means includesresilient means and fixed stop means positioned between said supportmeans and said illuminating means, said resilient means beingoperatively connected to said linkage means for providing a stableposition for said support means in which said object is loaded onto saidsupport means and for urging said support means toward said stop meanswhen said support means is moved from said stable position such thatsaid object is forced against said stop means and is retained thereby insaid predetermined position.

7. The apparatus of claim 1, further comprising support means foroperatively positioning said object in a manner such that said objectreflects the light from said illuminating means towards said lightsensitive means.

8. The apparatus of claim 7, further comprising linkage means for movingsaid support means to and from a predetermined position relative to saidilluminating means, and means cooperating with said linkage means formaintaining said predetermined position despite variations in the sizeof said object.

9. The apparatus of claim 8, wherein said maintaining means includesresilient means andstop means positioned between said support means andsaid illuminating means, said resilient means being operativelyconnected to said linkage means for providing a stable position for saidsupport means in which said object is loaded onto said support means andfor urging said support means toward said stop means when said supportmeans is moved from said stable position.

10. The apparatus of claim 9, wherein said maintaining means includesspacer means interposed between said support means and said stop meansfor determining said predetermined position.

1 l. The apparatus of claim 10, wherein said light sensitive means isoperatively mounted on said spacer means to receive light reflected fromsaid object.

12. The apparatus of claim 1 wherein a plurality of switch means arerespectively connected between the parallel outputs of said countermeans and a corresponding one of said circuit means for selectivelyinterrupting or passing each gate signal to the corresponding one ofsaid circuit means, and mode selector means for closing selective pairsof said switch means to pass the corresponding gate signals to thecorresponding circuit means, said mode selector means including meansfor selectively inactivating one of said circuit means.

13. Opticai measuring apparatus comprising support means for supportingan object to be optically analyzed, means for illuminating the objectsupported by said support means, a linkage means for moving said supportmeans toward and away from said illuminating means, stop means to limitthe motion of said support means towards said illuminating means toestablish a predetermined position for said object relative to saidilluminating means, a wall surrounding said object when said supportmeans has been moved by said linkage to place said object in saidpredetermined position, said wall spacing said support from said stopmeans to establish said predetermined position and blocking externallight from said object when said object is in said predeterminedposition, and light sensitive means mounted on said wall to receivelight reflected from said object when said object is in saidpredetermined position. v

1. Optical measuring apparatus, comprising a light source, a pluralityof optical filters, filter wheel means mounted for rotation between saidlight source and an object to be optically analyzed and carrying saidfilters for sequential registration thereof in the optical path betweensaid light source and said object, light sensitive means operativelypositioned to produce an output indicative of the light received fromsaid light source via said object, a logarithmic amplier operativelyreceiving the output of said light sensitive means, drive means forcausing regular rotation of said wheel means, first indexing meansformed on said filter wheel means for indicating each completerevolution of said wheel means, second indexing means formed on saidwheel means for indicating registration of each said filter in saidoptical path, means responsive to said first and second indexing meansfor providing corresponding first and second sinc signals, counter meansoperatively receiving said second sinc signal as a load input theretoand said first sinc signal as a reset input for producing paralleloutputs corresponding respectively to said filters, said counter meansproviding gate signals at each one of said parallel outputs when thecorresponding filter is in the optical path, a pair of sample and holdcircuit means each operatively receiving the output of said logarithmicamplifier and each controlled by a different one of said gate signals tosample the output of said logarithmic amplifier at times correspondingto the illumination of the object by light of one respective wavelength,and differential amplifier means operatively receiving the output ofeach of said circuit means for producing an output indicative of thedifference in optical density for the two respective wavelengths.
 2. Theapparatus of claim 1, wherein further including means for selectivelyinactivating one of said sample and hold circuit means so that theoutput of said differential amplifier is indicative of optical densityfor one of said filters.
 3. The apparatus of claim 1, further comprisingdigital display means, and analog to digital converter means operativelyreceiving said differential amplifier output for producing a digitaloutput to said display means.
 4. The apparatus of claim 1, furthercomprising support means for operatively positioning said object betweensaid illuminating means and said light sensitive means so that saidlight sensitive means produces an output indicative of the level oflight transmitted through said object.
 5. The apparatus of claim 4,further comprising linkage means for moving said support means to andfrom a predetermined position relative to said illuminating means, andmeans cooperating with said linkage means for maintaining said positiondespite variations in the size of said object.
 6. The apparatus of claim5, wherein said maintaining means includes resilient means and fixedstop means positioned between said support means and said illuminatingmeans, said resilient means being operatively connected to said linkagemeans for providing a stable position for said support means in whichsaid object is loaded onto said support means anD for urging saidsupport means toward said stop means when said support means is movedfrom said stable position such that said object is forced against saidstop means and is retained thereby in said predetermined position. 7.The apparatus of claim 1, further comprising support means foroperatively positioning said object in a manner such that said objectreflects the light from said illuminating means towards said lightsensitive means.
 8. The apparatus of claim 7, further comprising linkagemeans for moving said support means to and from a predetermined positionrelative to said illuminating means, and means cooperating with saidlinkage means for maintaining said predetermined position despitevariations in the size of said object.
 9. The apparatus of claim 8,wherein said maintaining means includes resilient means and stop meanspositioned between said support means and said illuminating means, saidresilient means being operatively connected to said linkage means forproviding a stable position for said support means in which said objectis loaded onto said support means and for urging said support meanstoward said stop means when said support means is moved from said stableposition.
 10. The apparatus of claim 9, wherein said maintaining meansincludes spacer means interposed between said support means and saidstop means for determining said predetermined position.
 11. Theapparatus of claim 10, wherein said light sensitive means is operativelymounted on said spacer means to receive light reflected from saidobject.
 12. The apparatus of claim 1 wherein a plurality of switch meansare respectively connected between the parallel outputs of said countermeans and a corresponding one of said circuit means for selectivelyinterrupting or passing each gate signal to the corresponding one ofsaid circuit means, and mode selector means for closing selective pairsof said switch means to pass the corresponding gate signals to thecorresponding circuit means, said mode selector means including meansfor selectively inactivating one of said circuit means.
 13. Opticalmeasuring apparatus comprising support means for supporting an object tobe optically analyzed, means for illuminating the object supported bysaid support means, a linkage means for moving said support means towardand away from said illuminating means, stop means to limit the motion ofsaid support means towards said illuminating means to establish apredetermined position for said object relative to said illuminatingmeans, a wall surrounding said object when said support means has beenmoved by said linkage to place said object in said predeterminedposition, said wall spacing said support from said stop means toestablish said predetermined position and blocking external light fromsaid object when said object is in said predetermined position, andlight sensitive means mounted on said wall to receive light reflectedfrom said object when said object is in said predetermined position.